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Re: [Qemu-devel] Segfault with coalesced mmio and boot CPU removal
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] Segfault with coalesced mmio and boot CPU removal |
Date: |
Wed, 27 Jul 2016 14:46:21 +1000 |
User-agent: |
Mutt/1.6.2 (2016-07-01) |
On Wed, Jul 27, 2016 at 10:01:41AM +0530, Bharata B Rao wrote:
> On Wed, Jul 27, 2016 at 08:22:51AM +0530, Bharata B Rao wrote:
> > Hi,
> >
> > Coalesced mmio buffer is part of vCPU 0's kvm_run mmap'ed area
> > and with the introduction of CPU hotplug, vCPU 0 can be removed on
> > PowerPC leading to the below seen segfault in QEMU.
> >
> >
> > This happens because during CPU removal, though we park the kvm_fd
> > corresponding to the removed vCPU thread, we unmap the kvm_run (and
> > hence coalesced mmio ring).
> >
> <snip>
> > What would be the best way to fix this ? Is disassociating
> > coalesced_mmio_ring
> > from vCPU 0's kvm_run the correct solution ?
>
> May be PowerPC too should do what x86 does like below for now ?
I think that's what we need to do short term. In the 2.8 timeframe,
separating the mmio ring out from the vcpu state sounds like a good
idea, but I don't really know how complicated that will be.
>
> commit 73360e27850b213327011f7e22e03865b8c0dd5b
> Author: Igor Mammedov <address@hidden>
> Date: Mon Jul 18 10:31:22 2016 +0200
>
> pc: Forbid BSP removal
>
> Boot CPU is assumed to always present in QEMU code, so
> untile that assumptions are gone, deny removal request,
> In another words QEMU won't support BSP hot-unplug.
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
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